1. Field of the Invention
The present invention relates to a resin composition comprising an ethylene-vinyl alcohol copolymer (EVOH) and a multi-layered structure comprising the resin composition. The resin composition has good interlayer adhesiveness when fabricated into laminates, and its moldings are yellowed little and have good appearance with few fish eyes (gels or hard spots) and streaks. While molded in melt, the resin composition ensures good long-run workability, and when recycled, it is yellowed little.
2. Description of the Related Art
EVOH is a useful polymer material having good oxygen barrier properties, oil resistance, antistatic properties and mechanical strength, and is widely used for various wrapping and packaging materials such as films, sheets, containers, etc. Such wrapping and packaging materials are generally produced by molding polymers in melt. Therefore, the polymers for them are required to have good long-run workability in melt molding (that is, they can be molded into good moldings with neither fish eyes nor streaks even in long-run molding lines), and their moldings are required to have good appearance (that is, they are yellowed little and have few fish eyes). Another important matter with such melt-molding polymers recently discussed is their recyclability. Concretely, in case where wastes of EVOH moldings are recovered and again molded in melt through repeated heat history, they are required to have good recyclability (that is, the recovered EVOH wastes have good moldability) and the recycled EVOH moldings are required to be yellowed little. In addition, for producing EVOH moldings with good mechanical strength, moisture resistance and heat-sealability, in general, EVOH is co-extruded together with a substrate of polyolefinic resin or the like to give multi-layered structures (e.g., laminates) in which the EVOH layer and the substrate resin layer are bonded to each other via an adhesive layer therebetween. In those structures, therefore, the interlayer adhesiveness between the constituent resin layers is an important factor. Specifically, the matters indispensable to such melt-molding polymers are that their moldings have good appearance, that they ensure good long-run workability in melt-molding lines, that they are recyclable, and that their laminates ensure good interlayer adhesiveness.
To meet the situation as above, various proposals have heretofore been made for producing good EVOH moldings by specifically processing EVOH with acids and/or metal salts, which include, for example, the following:
(1) An EVOH composition is disclosed, which contains from 0.0005 to 0.05% by weight (in terms of the metal) of a salt of a metal of Group 2 of the Periodic Table, from 0.002 to 0.2% by weight of an acid having a pKa of at least 3.5 and a boiling point of not lower than 180° C., and from 0.01 to 0.2% by weight of an acid having a pKa of at least 3.5 and a boiling point of not higher than 120° C., and having a specific melt viscosity (JP-A-66262/1989, U.S. Pat. No. 5,118,743). It is said that the EVOH composition with such additives has improved long-run workability and its moldings have good appearance with few fish eyes.
(2) Also disclosed is an EVOH resin composition, to which are added a hydroxycarboxylic acid and/or its salt, an alkali metal salt, an alkaline earth metal salt, a phosphate salt and a boron compound for improving the yellowing resistance, the appearance and the interlayer adhesiveness of the composition (JP-A-67898/1998). The EVOH resin composition of Example 1 in the laid-open specification contains, relative to 100 parts by weight of EVOH therein, 2000 ppm (in terms of the lactate radical) of lactic acid, 350 ppm (in terms of the metal element) of an alkali metal salt, 50 ppm (in terms of the metal element) of an alkaline earth metal, 30 ppm (in terms of the phosphorus element) of a phosphors compound, and 40 ppm (in terms of the boron element) of a boron compound. The EVOH resin composition of Comparative Example 7 therein contains, relative to 100 parts by weight of EVOH therein, 1230 ppm (in terms of the acetate radical) of acetic acid, 350 ppm (in terms of the metal) of sodium acetate, 50 ppm (in terms of the metal) of magnesium acetate, 30 ppm (in terms of the phosphorus element) of potassium dihydrogenphosphate, and 40 ppm (in terms of the boron element) of boric acid, and it is said that the films of the composition are yellowed and have some fish eyes, though having good interlayer adhesiveness.
(3) Disclosed is an EVOH composition, to which are added from 0.001 to 1% by weight (in terms of the boron element) of a boron compound, at most 0.05% by weight of acetic acid, from 0.001 to 0.05% by weight (in terms of the metal) of an acetic acid salt and/or from 0.0005 to 0.05% by weight (in terms of the phosphate radical) of a phosphate salt for improving the appearance, the long-run workability, the stretchability and the interlayer adhesiveness of the composition (WO99/05213, EP 930,339).
(4) Disclosed is an EVOH resin composition, to which are added from 0 to 1% by weight (in terms of boron element) of a boron compound, from 0 to 0.05% by weight of acetic acid, from 0 to 0.1% by weight (in terms of the metal) of sodium acetate, and from 0.001 to 0.02% by weight (in terms of the metal) of magnesium acetate and/or calcium acetate for improving the appearance, the long-run workability and the interlayer adhesiveness of the composition (JP-A-106592/1999, EP 906,924).
(5) Disclosed is an EVOH resin composition, to which are added from 0.05 to 0.3% by weight (in terms of the boron element) of a boron compound, from 0.001 to 0.02% by weight (in terms of the metal) of sodium acetate, and from 0.001 to 0.02% by weight (in terms of the metal) of magnesium acetate for improving the long-run melt-moldability of the composition to give transparent moldings with few fish eyes and streaks (JP-A-60874/1999).
In the related art disclosures (1) to (5), however, no one can find out an EVOH composition satisfying all the necessary requirements of long-run workability in melt molding, good appearance of moldings, recyclability, yellowing resistance in recycling, and interlayer adhesiveness in laminates. Highly functional EVOH moldings of high quality are needed these days, but, at present, none of known moldings are on the satisfactory level that meets the requirements.
Odorless EVOH resin compositions are desired for ensuring good working environments in producing them and in melting and molding them. Regarding the technique for reducing the smell of EVOH resin compositions, however, nothing is referred to in the related art disclosures.